Closed-loop clock synchronization

ABSTRACT

A network comprising a destination node, and a plurality of source nodes configured to transmit high-priority data and low-priority data to the destination node, wherein the source nodes correlate the transmission of the high-priority data to the destination node such that the high-priority data from each source node does not substantially contend with the high-priority data from the other source nodes upon arrival at the destination node. Also disclosed is a network component comprising at least one processor configured to implement a method comprising creating a periodic time window, partitioning the time window into low-priority time-bands and high-priority time-bands, placing a plurality of high-priority packets in the high priority time-bands, and placing a plurality of low-priority packets in the low-priority time-bands.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/971,386 filed Jan. 9, 2008 by Serge F. Fourcand and entitled“Closed-Loop Clock Synchronization”, which claims priority to U.S.Provisional Patent Application Ser. No. 60/886,833 filed Jan. 26, 2007by Serge F. Fourcand and entitled “Closed Loop Clock Synchronization,”both of which are incorporated herein by reference as if reproduced inits entirety.

This application is related to U.S. patent application Ser. No.11/735,590 filed Apr. 16, 2007 entitled “Inter-Packet Gap Network ClockSynchronization,” U.S. patent application Ser. No. 11/735,592 filed Apr.16, 2007 entitled “Network Clock Synchronization Timestamp,” U.S. patentapplication Ser. No. 11/735,596 filed Apr. 16, 2007 entitled“Multi-Frame Network Clock Synchronization,” and U.S. patent applicationSer. No. 11/735,598 filed Apr. 16, 2007 entitled “Network ClockSynchronization Floating Window and Window Delineation,” all of whichare by Serge F. Fourcand and are incorporated herein by reference as ifreproduced in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Ethernet is the preferred protocol for many types of networks because itis flexible, decentralized, and scalable. Ethernet is flexible in thatit allows variable-sized data packets to be transported across differenttypes of mediums using various nodes each having different transmissionspeeds. Ethernet is decentralized in that it allows the end devices totransmit and receive data without oversight or intervention from acentralized server or party. Furthermore, Ethernet is scalable in thatit can be implemented in both small-scale and large-scale networks.These advantages make Ethernet a preferred choice for data distributionin many computer networks.

Unfortunately, Ethernet does have some drawbacks. When Ethernet packetsare transported through the network, the Ethernet packets contend withother traffic being transported over the same links or through the samenodes. The contentious traffic not only includes packets bound for thesame destination, but also packets bound for other destinations that aretransported over the same link or through the same node as the Ethernetpacket. This contention produces burstiness and jitter at the nodeswithin the network. Some of these problems can be addressed by usingresource arbitration and buffers at the nodes, and by prioritizing thepackets into high-priority data and low-priority data. However, thesesolutions increase network complexity, increase delay, and detract fromthe inherent advantages of Ethernet.

The aforementioned drawbacks are part of the reason Ethernet has notbeen widely implemented in networks carrying high-priority data.Specifically, Ethernet does not provide a sufficient Quality of Service(QoS) to meet the stringent jitter and data loss requirements forstreaming audio and video data. Instead, high-priority data is carriedby highly synchronized networks, such as synchronous optical networks(SONET) and synchronous digital hierarchy (SDH) networks. VariousEthernet enhancements, such as circuit emulation, provider backbonetransport, and pseudowires, have been proposed to address the jitter anddata loss issues, but these enhancements fail to couple the flexibilityof Ethernet with the high QoS requirements of high-priority data. Thus,a need exists for an improved Ethernet protocol that is flexible, easyto implement, and supports the QoS requirements of high-priority data.

SUMMARY

In one aspect, the disclosure includes a network comprising adestination node, and a plurality of source nodes configured to transmithigh-priority data and low-priority data to the destination node,wherein the source nodes correlate the transmission of the high-prioritydata to the destination node such that the high-priority data from eachsource node does not substantially contend with the high-priority datafrom the other source nodes upon arrival at the destination node.

In another aspect, the disclosure includes a network componentcomprising at least one processor configured to implement a methodcomprising creating a periodic time window, partitioning the time windowinto low-priority time-bands and high-priority time-bands, placing aplurality of high-priority packets in the high-priority time-bands, andplacing a plurality of low-priority packets in the low-prioritytime-bands.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is an illustration of an embodiment of a closed-loop clocksynchronization method.

FIG. 2 is a schematic diagram of an embodiment of a packet switchednetwork.

FIG. 3 is an illustration of an embodiment of a method for enhancingpacket delivery.

FIG. 4 is an illustration of another embodiment of a method forenhancing packet delivery.

FIG. 5 is an illustration of another embodiment of a method forenhancing packet delivery.

FIG. 6 is an illustration of one embodiment of a general-purposecomputer system.

DETAILED DESCRIPTION

It should be understood at the outset that, although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems, methods, or both may be implemented using any numberof techniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the examples ofdesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

Disclosed herein is a system and method for enhancing service deliveryover packet switched networks using absolute time networksynchronization and inter-node synchronous scheduling. Specifically,absolute time network synchronization and inter-node synchronousscheduling may be combined to coordinate the transport of packets tonodes within a network such that the packets arrive at each node in astaggered manner. Transporting packets in a staggered manner maysubstantially reduce or eliminate packet contention at the destinationnode. With reduced contention, packets may experience less jitter andhence less delay and data loss. The system and method may support thetransport of current standard packet traffic, as well as emergingconstant bit rate (CBR) traffic that may require higher QoS and have alower tolerance for jitter and data loss. In a specific embodiment, thesystem and method may support the distribution of time divisionmultiplexed (TDM) and fixed bandwidth traffic such as real-time audioand video applications over packet switched networks.

The nodes described herein may be any devices that forward packets tosimilar devices within a packet switched network. The nodes may be theoriginator or ultimate recipient of the packets or may merely forwardreceived packets to other nodes. In some embodiments, the nodes mayselect paths for the individual packets to travel over the packetswitched network. The nodes may have different properties, such asphysical structure, capacity, transmission speed, and so forth. Thenodes may be internal network devices such as routers, switches, orbridges, or the nodes may be user-oriented devices such as desktopcomputers, notebook computers, personal digital assistants (PDAs), orcellular telephones.

To support the enhanced service delivery described herein, at least someof the nodes within the network must be able to synchronize their clockswith the clocks in other nodes within the network, a process referred toherein as absolute time network synchronization. While any clocksynchronization method may be used to achieve absolute time networksynchronization between the nodes, FIG. 1 illustrates a diagram of asystem 100 that utilizes a closed-loop clock synchronization scheme toachieve absolute time synchronization between a first node 102 and asecond node 104. In the closed-loop clock synchronization scheme shownin FIG. 1, packet timestamps are used to achieve absolute time networksynchronization between the first node 102 and the second node 104.Specifically, an upstream synchronization timestamp 106 may be createdat the first node 102 and transmitted at time T₁ to the second node 104.Due to the transit time D₁ between the first node 102 and the secondnode 104, the upstream synchronization timestamp 106 may be received attime T₂ by the second node 104. The second node 104 may process theupstream synchronization timestamp 106 and create a downstreamsynchronization timestamp 108 that references the upstreamsynchronization timestamp 106. The processing at the second node 104results in a delay D₂ between T₂ and T₃. The downstream synchronizationtimestamp 108 may then be transmitted back to the first node 102 inanother packet at time T₃. Due to the transit time D₃ between the secondnode 104 and the first node 102, the downstream synchronizationtimestamp 108 may be received at time T₄ by the first node 102. Thefirst node 102 may then compare the upstream synchronization timestamp106 and the downstream synchronization timestamp 108 to determine theround-trip packet delay D₄.

In some embodiments, it may be assumed that there are symmetric upstreamand downstream transit times between the first node 102 and the secondnode 104. In such a case, the upstream packet transit time D₁ may besubstantially equal to the downstream packet transit time D₃.Consequently, the transit time D₁ may be calculated by subtracting theinternal processing delay D₂ from the round-trip packet delay D₄, anddividing the difference by two. The internal processing delay D₂ may bedetermined by subtracting the time T₂ from the time T₃, and thetimestamp round-trip delay may be determined by subtracting the time T₁from the time T₄. Thus, the transit time D₁ may be estimated usingequation 1:D ₁=[(T ₄ −T ₁)−(T ₃ −T ₂)]/2  (1)

The transit time D₁ may be used to synchronize the second node's clockwith the first node's clock. Specifically, the transit time D₁ and thefirst node's clock timing may be sent to the second node 104 so that thesecond node 104 can synchronize its clock with the first node's clock.Alternatively, the first node 102 may use the transit time D₁ and thedownstream synchronization timestamp 108 to synchronize its clock withthe second node's clock. The system 100 may recalculate the transit timeD₁ and resynchronize the clocks over regular time intervals to improvethe estimation of the transit time D₁. An embodiment of the closed-loopclock synchronization scheme shown in FIG. 1 is described in furtherdetail in U.S. patent application Ser. No. 11/735,590 filed Apr. 16,2007 by Serge F. Fourcand and entitled “Inter-Packet Gap Network ClockSynchronization,” which is incorporated by reference herein as ifreproduced in its entirety.

The above-described clock synchronization method is not the only methodby which the nodes may achieve absolute time network synchronization.Specifically, absolute time network synchronization may be implementedbetween the first node 102 and the second node 104 using the methodsdescribed in Institute for Electrical and Electronic Engineers (IEEE)standard 1588. Alternatively, absolute time network synchronization maybe implemented between the first node 102 and the second node 104 usingany other absolute time synchronization scheme. Moreover, the conceptsdescribed herein may be repeated over a plurality of nodes such thatthree or more nodes are able to achieve absolute time networksynchronization with each other. In an embodiment, some of the nodes inthe group may implement one clock synchronization method while othernodes in the group may implement different clock synchronization methodsto share the same absolute time.

Once the nodes share a common absolute time and are aware of the transittimes between nodes, the nodes may coordinate the transport of packetswithin the network. Specifically, a plurality of source nodes maydispatch packets to a common destination node in a time-correlatedmanner such that the packets do not arrive simultaneously at thedestination node, a process referred to herein as inter-node synchronousscheduling. Nodes that participate in inter-node synchronous schedulingare referred to herein as participating nodes. As part of the inter-nodesynchronous scheduling, the participating nodes communicate with eachother or a third party and identify transmission time-bands for eachnode, data type, or both. By using the assigned time-bands andaccounting for the transit time to the destination node, theparticipating nodes are able to coordinate the transport of packets tothe destination node and substantially reduce or eliminate contention atthe destination node.

FIG. 2 illustrates one embodiment of a communication network 200utilizing inter-node synchronous scheduling to coordinate the dispatchof packets from different source nodes to a common destination node. Thenetwork 200 may comprise nodes 202, 204, 206, and 210 that may supportabsolute time synchronization. As shown in FIG. 2, the transport delaybetween node 202 and node 210 is D₁, the transport delay between node204 and node 210 is D₂, and the transport delay between node 206 andnode 210 is D₃. Although the network 200 is shown to comprise fourparticipating nodes and one non-participating node, the network 200 maycomprise any number of participating and non-participating nodes.

The network 200 may also comprise a node 208 that may not supportabsolute time synchronization, referred to herein as a non-participatingnode. Without implementing absolute time synchronization, the transittime between each of the three source nodes 202, 204, and 206 and thenon-participating node 208 may not be estimated. Hence, no directinter-node synchronous scheduling may be implemented for packetstransmitted from the three source nodes 202, 204, and 206 when thenon-participating node 208 is the destination node. However, when thereis a single path between the non-participating node 208 and thedestination node, packets may arrive at the destination node 210 in thesame order that they arrive at the non-participating node 208. Thenon-participating node 208 need not be connected to all of the sourcenodes 202, 204, 206 so long as any delay in the non-participating nodesis accounted for in the inter-node synchronous scheduling. Thus, packetsthat are dispatched from the three source nodes 202, 204, and 206 to thedestination node 210 may arrive at the non-participating node 208 in astaggered manner, and thus may undergo minimal contention at thenon-participating node 208.

Nodes 202, 204, 206 may send packets with various priority levels tonode 210. As an example, these packets may be classified ashigh-priority packets (HPPs) and low-priority or best effort packets(BEPs). Additional priority levels may be used. The priority levels ofthe packets may be determined based on the QoS requirements of the datawithin the packet or some service level agreement (SLA) associated withthe packet. Specifically, HPPs may comprise data with high QoSrequirements, such as TDM data or streaming audio/video data. Incontrast, BEPs may comprise services with low or no QoS requirements,such as Internet Protocol (IP) packets used for web browsers and emailpackets.

As shown in FIG. 2, the nodes 202, 204, 206 may each be assigned aseries of time-bands for the different priority levels of traffic.Specifically, the nodes 202, 204, 206 may each be assigned time-bandsfor transmitting HPPs to the destination node 210, designated as HP inFIG. 2. The nodes 202, 204, 206 may also be assigned time-bands fortransmitting BEPs to the destination node 210, designated as LP in FIG.2. Each of the source nodes 202, 204, and 206 may dispatch their HPPsand BEPs to the destination node 210 using the HP and LP time-bands,respectively. The inter-node synchronous scheduling may rely on theabsolute time network synchronization between the nodes 202, 204, 206,210 to coordinate packet dispatch from different source nodes 202, 204,206 to the common destination node 210. In addition, the nodes 202, 204,206 may dispatch their packets such that the HP time-bands do notoverlap or have a substantially reduced overlap, whereas the LPtime-bands may overlap. Specifically, node 202 uses time offset P₁, node204 uses time offset P₂, and node 206 uses time offset P₃ to adjusttheir transmissions to align each of the HPPs such that they do notcontend with each other upon arrival at the non-participating node 208or the destination node 210. This arrangement is shown by the offsetalignment of HP time-bands from nodes 202, 204, 206. Hence, packetcontention over the shared resources of the destination node, forexample a common memory buffer, may be substantially reduced oreliminated. As used herein, the term contention refers to thesimultaneous arrival of HPPs from a plurality of source nodes at acommon port at destination node. In an embodiment, a scheduler withinthe source nodes manages the transmission of the data streams within thetime-bands using the time offsets.

The inter-node synchronous scheduling described herein may be modifiedto suit many different situations. For example, varying the quantity andsizes of the HP and LP time-bands within a periodic window may controlthe high-priority and low-priority traffic bandwidths in the network200. In some instances, two or more distinct data flows of the samepriority level but with different bandwidth sizes may be dispatched fromthe same source node. Within each flow, the packets may have differentsizes. Alternatively, three or more priority levels may be considered,wherein three or more types of time-bands may be assigned to thepriority levels. Packets with three or more priority levels may bedispatched from a source node over their assigned time-bands in asimilar manner to the two-priority level.

Although the inter-node synchronous scheduling provides a framework fortransporting HPPs from a plurality of source nodes to a singledestination node without substantial contention at the source node,there may be a need for variations of the framework. Specifically,because packets can be different sizes, received at infrequentintervals, or both, the time-bands may not be filled or the packets mayoverrun the time-bands. Described below are three operational modes foraddressing such circumstances, termed the Huawei Enhanced ProviderBackbone Bridged (HE-PBB)-1 operational mode, the HE-PBB-2 operationalmode, and the HE-PBB-3 operational mode.

FIG. 3 is an illustration of one embodiment of a system 300 implementingthe HE-PBB-1 operational mode. The system 300 implements a periodic,reoccurring window between each source node and each destination node.The window may have any duration, such as 125 microseconds (μs). Withinthe window, several different time-bands may be defined, such as theaforementioned HP and LP time-bands. As described above, the HPtime-bands between a source node and a destination node may notsubstantially overlap with HP time-bands assigned between other sourcenodes and the same destination node. The system 300 may associate all ofthe HP time-bands within a single periodic window to a single HPP flow.However, the source node may process more than one stream of HPP, andmay send more than one stream of HPP to a single destination node. Assuch, the source node may associate the HP time-bands within a periodicwindow with a plurality of HPP flows, designated as HP₁ . . . HP_(x) inFIG. 3. In such a case, the individual HP time-bands may be used todifferentiate the HPP flows, or the HPP flows may be differentiatedbased on information within the packets' headers. In addition, the sizeand quantity of HP time-bands associated with each HPP flow may bevaried to define a desired amount of bandwidth from the source node tothe destination node.

As mentioned above, the periodic window may also contain one or more LPtime-bands. In contrast with the HP time-bands, the LP time-bandsbetween a source node and a destination node are assigned without regardto the LP time-bands between other source nodes and the destinationnode. Consequently, the LP time-bands between a source node and adestination node may overlap with LP time-bands assigned between othersource nodes and the same destination node. BEPs are generally processedindividually, and thus are not generally associated with a particularflow. However, if it is desired to associate BEPs with a BEP flow, thenthe source node may associate the LP time-bands within a periodic windowwith one or more BEP flows. As with the HP time-bands, the individual LPtime-bands may be used to differentiate the BEP flows, or the BEP flowsmay be differentiated based on information within the packets' headers.In addition, the size and quantity of LP time-bands associated with eachBEP flow may be varied to define a desired amount of bandwidth from thesource node to the destination node. In addition, the LP time-bands maysimply be any time-bands not designated as HP time-bands, or the LPtime-bands may be a separate designation such that the periodic windowmay contain HP, LP, and idle time-bands.

In some instances, an HPP may exceed the length of its assigned HPtime-band. Specifically, due to the variable size of the packets, thedispatch of a single packet may exceed a single time-band to which thepacket was assigned. For example and with reference to FIG. 3, thesource node may dispatch two consecutive HPPs 302, 304, bothcorresponding to HP time-band 320. However, HP time-band 320 may not belarge enough to accommodate the two consecutive HPPs 302, 304, and thusHPP 304 overruns HP time-band 320 and encroaches some of the adjacent LPtime-band 322. The system 300 may allow HPP 304 to encroach some of LPtime-band 322 in such instances. Such may be preferable because: HPPshave a higher priority level than BEPs, it may be undesirable to breakup HPP 304, dispatching the HPPs without tolerating some HPPencroachment over LP time-bands may cause intolerable delivery delays inHPPs, or combinations thereof. The encroaching HPP flow may cause delaysin BEP delivery to the destination node. However, such BEP deliverydelay may be tolerated to ensure no or minimal delivery delays of HPPsand because BEPs have a low-priority level. After dispatch of the HPP isconcluded, the source node may begin dispatching the packets associatedwith the LP time-band 322.

In an embodiment, the source node may balance the HPP encroachment intoLP time-bands by allowing the BEPs to encroach on the HP time-bands.Specifically, the overrun of HPPs into LP time-bands gives the HPP flowmore bandwidth than is allocated in the HP time-bands. The extent of theadditional bandwidth may be tracked, for example, by the source node oranother network component by keeping a running total of the length ofeach overrun. When such overruns reach a certain point, such as the sizeof a BEP, the source node may compensate for such overruns by allowing aBEP to replace an HPP in an HP time-band. For example and with referenceto FIG. 3, HPP 308 would normally be sent in HP time-band 324. However,BEP 306 can replace HPP 308 to compensate for previous or anticipatedHPP overruns. The BEP 306 may be dispatched wholly within the HPtime-band 324, or may overrun into the adjacent LP time-band 326. Whenmultiple HP time-bands associated with different HPP flows are present,the HPP flows' overruns may be tracked as a group, or each HPP flow maybe tracked individually and BEP replacement of HPPs allocated on aflow-by flow basis. In any event, the encroachment of the BEP in the HPtime-band is tracked and deducted from the running total of HPP overrun.

In an embodiment, the different HP time-bands are separated by LPtime-bands. When two HP time-bands associated with the same HPP flow areadjacent to one another and the HPPs exceed the first HP time-band, theencroachment of the HPPs on the second time-band has no effect on thebandwidth allocated to the HPP flow. However, when two HP time-bandsassociated with different HPP flows are adjacent to one another and thefirst HPP flow exceeds the first HP time-band, the first HPP flowencroaches on the bandwidth of the second HPP flow and jitter may occur.When such encroachment persists, the bandwidth of the second HPtime-band may suffer, and may eventually cause packet losses due tomemory queue overflow. Therefore, it may be necessary to separatedifferent HP time-bands by one or more LP time-bands, keeping in mindthat additional LP time-bands within the periodic window reduce the linkutilization in terms of HPP transmission bandwidth.

In some instances, a BEP may exceed the length of its assigned LPtime-band. For example and with reference to FIG. 3, the source node maydispatch BEP 310 corresponding to LP time-band 328. However, LPtime-band 328 may not be large enough to accommodate the BEP 310, andthus BEP 310 overruns LP time-band 328 and encroaches some of theadjacent HP time-band 330. Alternatively, the HPP 316 may be sent latedue to jitter. The system 300 may allow BEP 310 to encroach some of HPtime-band 330 in such instances. Such may be preferable because it maybe undesirable to break up BEP 310, but the encroaching BEP flow maycause delays in HPP delivery to the destination node. As such, the BEPoverruns may be tracked and corrected in a manner similar to thatdescribed above for HPP overruns. After dispatch of the BEP isconcluded, the source node may begin dispatching the packets associatedwith the HP time-band 330.

In some instances, there may be idle periods when there are not any BEPor HPP to dispatch. Such instances occur, for example, when there is aninter-packet gap (IPG). In such instances, the source node may dispatcheither an HPP or a BEP whenever it is ready and without regards to theclassification of the time-band as HP or LP. For example and withreference to FIG. 3, an IPG 312 occurs in LP 332 and the source node issubsequently ready to dispatch HPP 314. In such a case, HPP 314 may bedispatched prior to the beginning of HP time-band 324. Thus, some HPPsmay occupy the end portion of a LP time-band that precedes the assignedHP time-band, a condition referred to as an underrun. A similarsituation may exist when BEPs underrun their LP time-band and encroachan HP time-band during an idle period. In either case, the underruns maybe tracked and corrected as described above. The described underruns andoverruns may improve link bandwidth utilization while keeping packetdelays and jitter at a minimum. In an embodiment, the length of theoverruns and underruns described herein correlate to the jitter allowedwithin the system 300.

FIG. 4 is an illustration of one embodiment of a system 400 implementingthe HE-PBB-2 operational mode. As with the HE-PBB-1 operational mode,the system 400 may use absolute time synchronization and inter-nodesynchronous scheduling between a participating source node and aparticipating destination node. The system 400 may also implement aperiodic, reoccurring window between each source node and eachdestination node, and several different priority level time-bands may bedefined within the window. The properties of the periodic window and thetime-bands are substantially the same as described above. However,unlike the HE-PBB-1 operational mode, the HE-PBB-2 operational modetruncates and encapsulates some of the packets to make the packets fitwithin the time-bands.

FIG. 4 illustrates the truncation and encapsulation that occurs withinthe source node. Specifically, the top and bottom rows of FIG. 4illustrate an incoming stream of BEPs 450 and HPPs 458, respectively.The BEPs 450 and HPPs 458 are arranged in the temporal order that theyare received at the source node such that BEPs 450 and HPPs 458 on theleft side of FIG. 4 are received before BEPs 450 and HPPs 458 on theright side of FIG. 4. As explained below, the BEPs 450 are truncated andencapsulated into a modified BEP stream 452. Similarly, the HPPs 458 aretruncated and encapsulated into a modified HPP stream 456. Thearrangement of the HP, LP, and idle time-bands within the periodic timewindow is shown in the packet allocation 454. After each packet in themodified BEP stream 452 and the modified HPP stream 456 is created, itis added to the packet allocation 454 in the appropriate time-band, e.g.modified BEPs 452 in LP time-bands and modified HPPs 456 in HPtime-bands. Thus, the packet allocation 454 represents the outgoing datastream. The process illustrated in FIG. 4 may be implemented in reverseat the destination node to unencapsulate and recombine the packetallocation 454 into the original BEPs 450 and HPPs 458.

The truncation and encapsulation of the BEPs 450 and HPPs 458 issubstantially the same, and can be illustrated using HPPs 402, 404, 406and modified HPPs 408 and 410. As HPPs 402, 404 are received by thesource node, they are encapsulated within the modified HPP 408.Specifically, a new header is created for modified HPP 408 using astandard header, such as the Layer 2 framing used in Ethernet networks.In addition, the modified HPP 408 may use a standard packet size, whichmay be any acceptable packet size, including standard Ethernet framesizes and jumbo Ethernet frame sizes. The standard header and packetsize allows the modified HPPs 456 and modified BEPs 452 to be tunneled,routed, and otherwise processed by non-participating nodes. In addition,it would be desirable to optimize the size of the HP time-bands, LPtime-bands, the modified BEPs 452 and the modified HPPs 456 such thatthe time-bands match the correlating modified packets to minimize theoverhead due to the required second level of framing. However, this mayhave to be balanced with the requirements for bandwidth granularity andthe desired number of time-bands that have to be supported.

After the standard header is created, the HPPs 402, 404 are added to thedata section of the modified HPP 408 until the data section is filledsuch that the modified HPP 408 has a standard packet size. As shown inFIG. 4, then an entire HPP 404 may not be able to fit into a singlemodified HPP 408. As such, the HPP 404 is truncated such that the firstportion of HPP 404, e.g. the portion to the left of the dashed line, isadded to the modified HPP 408. The remaining portion of the HPP 404,e.g. the portion to the right of the dashed line, is buffered in amemory and later combined with HPP 406 in modified HPP 410. If desired,special control characters may be placed within the modified HPP 408 todelineate one HPP 458 from another, e.g. HPP 402 from HPP 404. Inaddition, special control characters may be placed within the modifiedHPPs 456 to indicate the continuation of a previous HPP 458, e.g. thesecond portion of HPP 404 in modified HPP 410, if desired. Thetruncation and encapsulation described herein may be preferable becausethe modified HPPs 456 and modified BEPs 452 may be substantially thesame size as the time-bands in the packet allocation 454.

In some embodiments, there may be instances when only one of the BEPstream and the HPP stream is being received by the source node during anon-corresponding time-band. For example, BEP 412 may be received at atime corresponding to the HP time-band 416, but no HPPs 458 are beingreceived or buffered for subsequent encapsulation. In such a case, it isnot desirable to buffer the BEP 412 and let the packet allocation 454 goidle. As such, when only one packet stream is being received during anon-corresponding time-band, that packet stream may be placed into thenon-corresponding time-band for transmission to the destination node.Specifically, BEP 412 and the first part of BEP 418 can be encapsulatedinto modified BEP 414, which is then placed into the unused portion ofHP time-band 416, e.g. the portion to the right of the dashed line, andLP time-band 420. If desired, a special control character may be used toindicate the presence of the modified BEP 452 in the HP time-band 416.It will be appreciated that this embodiment may also be implemented atthe beginning of a non-corresponding time-band. In addition, the presentembodiment may also be used for placing modified HPPs 456 into LPtime-bands. Placing a packet stream into a non-corresponding time-bandmay be preferable because it may increase the utilization of the linkbetween the source node and the destination node.

In some embodiments, BEPs 450 and HPPs 458 may be received alternativelyin a limited overlapping manner. For example, BEPs 432, 434 are receivedand followed by HPP 430. As shown in FIG. 4, there may be some overlapbetween BEP 434 and HPP 430. As such, BEP 434 would normally contendwith HPP 430, and would have to be truncated because HPP 430 has therights to HP time-band 426. However, some delay may be incurred inencapsulating HPP 430 within modified HPP 428. As such, modified BEP 422may be placed in LP time-band 424 and the first portion of HP time-band426 until modified HPP 428 is complete. Upon the completed encapsulationof modified HPP 428, the modified BEP 422 is placed in the secondportion of HP time-band 426. Thus, even though there was some initialcontention between BEP 434 and HPP 430, the contention was resolvedduring the encapsulation and placement of modified BEP 422 and modifiedHPP 428 into HP time-band 426. This contention delay may correspond tothe jitter allowed within the system 400. It will be appreciated thatBEP 434 may be truncated such that the modified BEP 422 does not contendwith the modified HPP 428 for the HP time-band 426. It will also beappreciated that this embodiment may occur in the reverse order suchthat a modified BEP is subsequent to a modified HPP. Finally, thepresent embodiment is also applicable to HPPs 458 contending with BEPs450 for LP time-bands.

In some embodiments, a plurality of similar time-bands may be adjacentto one another. For example, LP time-bands 446 and 448 are adjacent toone another in FIG. 4. In such cases, it may not be necessary for themodified BEPs 452 or modified HPPs 456 to be sized such that they alignwith the time-bands. Specifically, because LP time-bands 446 and 448 areassigned to carry the same data type, modified BEPs 436, 438, and 440may be placed in LP time-bands 446 and 448. Alternatively, BEPs 442 and444 could be placed in LP time-bands 446 and 448, if desired.

FIG. 5 is an illustration of one embodiment of a system 500 implementingthe HE-PBB-3 operational mode. As with the previous operational modes,the system 500 may use absolute time synchronization and inter-nodesynchronous scheduling between a participating source node and aparticipating destination node. The system 500 may also implement aperiodic, reoccurring window between each source node and eachdestination node, and several different priority level time-bands may bedefined within the window. The properties of the periodic window and thetime-bands are substantially the same as described above. However,unlike the other operational modes, the HE-PBB-3 operation mode uses aspecial control character to delineate the transition between packettypes, e.g. BEP and HPP, and truncates the packets at the end of thecorresponding time-band, e.g. HP or LP.

FIG. 5 illustrates the delineation and truncation that occurs within thesource node. Specifically, the bottom two rows of FIG. 5 illustrateincoming streams of HPPs 524 and BEPs 526. The HPPs 524 and BEPs 526 arearranged in the temporal order that they are received at the source nodesuch that HPPs 524 and BEPs 526 on the left side of FIG. 5 are receivedbefore HPPs 524 and BEPs 526 on the right side of FIG. 5. As explainedbelow, the HPPs 524 and BEPs 526 are truncated and fit into a modifiedpacket stream 522. The arrangement of the HP, LP, and idle time-bandswithin the periodic time window is shown in the packet allocation 520.After the HPPs 524 and BEPs 526 are fit into the modified packet stream522, the modified packet stream 522 is added to the packet allocation520. Thus, the packet allocation 520 represents the outgoing datastream. The process illustrated in FIG. 5 may be implemented in reverseat the destination node to reconstruct the original HPPs 524 and BEPs526.

In the system 500, the beginning of each packet type is indicated by aspecial control character. Specifically, an HPP start character 506 isplaced in the modified packet stream 522 before HPPs 502 and 504. Usingthe special Ethernet control symbol, the system 500 may be utilized toenforce SLAs, wherein the levels of service availability are specified.Using the special Ethernet control symbols to truncate the HPPs may alsoallow the use of contiguous HP time-bands while minimizing contentionbetween HPPs at the participating nodes. The alignment of the HPP startcharacter 506 and the HPPs 502, 504 in the modified packet stream 522corresponds to the size and location of the HP time-band 510. Any BEPs526 received during the HP time-bands are buffered until the next LPtime-band 512. As such, HPP 504 is truncated at the end of HP time-band510, buffered, and inserted into the modified packet stream 522 at thenext HP time-band 514. When LP time-band 512 begins, a BEP startcharacter 508 is inserted into the modified packet stream 522 and isfollowed by BEP 516. It will be appreciated that the BEPs 526 may betruncated in a similar manner as the HPPs 524.

The HE-PBB-3 operational mode may be advantageous for many reasons. Forexample, the HE-PBB-3 operational mode may prevent HPPs from encroachingon LP time-bands and BEPs from encroaching on HP time-bands. Since thereare no encroachment issues, the packets are the same size as theircorresponding time-bands minus the special Ethernet control symboloverhead, and hence optimal bandwidth utilization for HPPs may beachieved. The special Ethernet control symbol may also minimizeBEP-to-HPP transition overhead. Because of reduced overhead duringtransitions between HPPs and BEPs, the system 500 may reduce the size oftime-bands in the periodic time window without significant bandwidthloss. Reducing the size of time-bands in the periodic time window mayfurther improve bandwidth granularity and enable the support of a largernumber of time-bands. By supporting a larger number of time-bands withinthe periodic time window, the system 500 may support a larger number oflogical data flows through the network.

Unlike the HE-PBB-1 and HE-PBB-2 operational modes, the HE-PBB-3operational mode may not support the transition of the truncated HPPsand BEPs through non-participating nodes in the network. Thenon-participating nodes may not recognize the non-standard specialEthernet control symbols that are used in the truncated frames. For thatreason, forwarding and terminating the truncated HPPs and BEPs may bedone by the participating nodes of the system 500 that recognize thespecial Ethernet control symbols. The truncated frames may be forwardedusing equipments compatible with standard Layer 1 Ethernet frames. Theuse of the special Ethernet control symbols may be sufficient forenhancing packet distribution and delivery with no furtherencapsulation, which may improve links utilization without the need fora Layer 2 Ethernet framing.

In comparison to the HE-PBB-1 and HE-PBB-2 operational modes, theHE-PBB-3 operational mode may involve less complexity in the decisionlogic required to handle the wide range of Ethernet packet sizes. In oneembodiment, the system 500 may utilize the closed-loop clocksynchronization method described above for absolute timesynchronization, which may require a full-duplex mode of implementation.The full-duplex mode of implementation may also be utilized by thesystem 500 for preamble or header suppression to increase the availablelink bandwidth.

The network described above may be implemented on any general-purposenetwork component, such as a computer or network component withsufficient processing power, memory resources, and network throughputcapability to handle the necessary workload placed upon it. FIG. 6illustrates a typical, general-purpose network component suitable forimplementing one or more embodiments of a node disclosed herein. Thenetwork component 600 includes a processor 602 (which may be referred toas a central processor unit or CPU) that is in communication with memorydevices including secondary storage 604, read only memory (ROM) 606,random access memory (RAM) 608, input/output (I/O) devices 610, andnetwork connectivity devices 612. The processor may be implemented asone or more CPU chips, or may be part of one or more applicationspecific integrated circuits (ASICs).

The secondary storage 604 is typically comprised of one or more diskdrives or tape drives and is used for non-volatile storage of data andas an over-flow data storage device if RAM 608 is not large enough tohold all working data. Secondary storage 604 may be used to storeprograms that are loaded into RAM 608 when such programs are selectedfor execution. The ROM 606 is used to store instructions and perhapsdata that are read during program execution. ROM 606 is a non-volatilememory device that typically has a small memory capacity relative to thelarger memory capacity of secondary storage. The RAM 608 is used tostore volatile data and perhaps to store instructions. Access to bothROM 606 and RAM 608 is typically faster than to secondary storage 604.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. A network component comprising: a processorconfigured to: determine aperiodic transmission window to transmit data;partition the periodic transmission window into a plurality oflow-priority time-bands and a plurality of high-priority time-bands;receive a plurality of high-priority packets and a pluralitylow-priority packets; truncate at least one of the high-priority packetsand one of the low-priority packets; encapsulate the high-prioritypackets and the low-priority packets; and an output device coupled tothe processor, wherein the output device is configured to: transmit aremainder of the truncated high-priority packet in a subsequenthigh-priority time-bands; transmit a remainder of the truncatedlow-priority packet in a subsequent low-priority time-bands; transmitthe encapsulated high-priority packets during the high-prioritytime-bands; and transmit the encapsulated low-priority packets duringthe low-priority time-bands, wherein the high-priority time bandsrepresent assigned time intervals within the periodic transmissionwindow designated for the transmission of the encapsulated high-prioritypackets, wherein at least some of the low-priority packets and some ofthe high-priority packets are received simultaneously, and wherein thetransmission for the encapsulated low-priority packets and theencapsulated high-priority packets do not overlap.
 2. The networkcomponent of claim 1, wherein some of the high-priority packets and someof the low-priority packets are not truncated, and wherein thelow-priority time bands represent assigned time intervals within theperiodic transmission window designated for the transmission of thelow-priority packets.
 3. The network component of claim 1, wherein thehigh-priority packets belong to a plurality of high-priority flows, andwherein there is at least one high-priority time-band for eachhigh-priority flow.
 4. The network component of claim 1, wherein theprocessor is further configured to: fill some of the high-prioritytime-bands with encapsulated low-priority packets when there are not anyencapsulated high-priority packets to place in the high-prioritytime-bands; and fill some of the low-priority time-bands withencapsulated high-priority packets when there are not any encapsulatedlow-priority packets to place in the low-priority time-bands.
 5. Thenetwork component of claim 1, wherein the processor is furtherconfigured to: delineate the start of the high-priority packets with acontrol symbol; and delineate the start of the low-priority packets withanother control symbol.
 6. The network component of claim 1, wherein theoutput device is further configured to transmit part of the truncatedhigh-priority packet within a first high-priority time-band.
 7. Thenetwork component of claim 6, wherein the remainder of the truncatedhigh-priority packet is not transmitted within the first high-prioritytime-band.
 8. The network component of claim 1, wherein an offset isused to align the high-priority time-bands with a second set ofhigh-priority time-bands.
 9. The network component of claim 8, whereinthe second set of high-priority time-bands are used by a differentsource node to transmit a second set of high-priority packets, andwherein the high-priority time-bands and the second set of high-prioritytime-bands do not overlap within the periodic transmission window. 10.The network component of claim 1, wherein a first high-priority packetis assigned to a first high-priority time-band, wherein some of thefirst high-priority packet is transmitted within the first high-prioritytime-band, and wherein some of the first high-priority packet istransmitted within a first low-priority time-band immediately followingthe first high-priority time-band.
 11. The network component of claim 1,wherein a first encapsulated low-priority packet is transmitted within afirst high-priority time-band during encapsulation of a firsthigh-priority packet that is assigned to the first high-prioritytime-band.
 12. A method for coordinating the dispatch of data from oneor more source nodes to a common destination node, wherein the methodcomprises: establishing a periodic time window; and receiving a firstdata stream that comprises a plurality of first high-priority packetsand a plurality of first low-priority packets within the periodic timewindow, wherein the first high-priority packets are received within aplurality of first high-priority time-bands for the first data stream,wherein the first low-priority packets are received within a pluralityof first low-priority time-bands for the first data stream, wherein thefirst high-priority time-bands represent assigned time intervals withinthe periodic time window designated for the transmission of the firsthigh-priority packets, wherein the first low-priority time-bandsrepresent assigned time intervals within the periodic time windowdesignated for the transmission of the first low-priority packets,wherein at least one of the high-priority packets and one of thelow-priority packets are truncated within the data stream, wherein aremainder of the truncated high-priority packet is placed in asubsequent first high-priority time-bands, wherein a remainder of thetruncated low-priority packet is placed in a subsequent firstlow-priority time-bands, wherein the first high-priority packets and thefirst low-priority packets are encapsulated within the data stream,wherein some of the first low-priority packets and some of the firsthigh-priority packets are received simultaneously by one of the sourcenodes, and wherein the first low-priority packets and the firsthigh-priority packets do not overlap within the data stream.
 13. Themethod of claim 12 further comprising receiving a second data streamthat comprises a plurality of second high-priority packets and aplurality of second low-priority packets, wherein the secondhigh-priority packets are received within a plurality of secondhigh-priority time-bands for the second data stream, wherein the secondhigh-priority time-bands represent assigned time intervals within theperiodic time window designated for the transmission of the secondhigh-priority packets, and wherein the first high-priority time-bandsand the second high-priority time-bands do not overlap.
 14. The methodof claim 13 further comprising receiving a second data stream thatcomprises a plurality of second high-priority packets and a plurality ofsecond low-priority packets, wherein the second low-priority packets arereceived within a plurality of second low-priority time-bands for thesecond data stream, wherein the second low-priority time-bands representassigned time intervals within the periodic time window designated forthe transmission of the second low-priority packets, and wherein thefirst low-priority time-bands and the second low-priority time-bandsoverlap.
 15. The method of claim 14, wherein the first low-prioritypackets and first high priority packets are encapsulated using an OpenSystems Interconnection (OSI) layer 2 header, wherein a firstencapsulated low-priority packet comprises a portion of the truncatedlow-priority packet, and wherein a second encapsulated low-prioritypacket comprises a remaining portion of the truncated low-prioritypacket.
 16. The method of claim 12 further comprising: delineating thestart of the first high-priority packet with a start special character;and delineating the start of the first low-priority packet with a secondstart special character.